1. Field of the Invention
The present invention relates to an image compressing device, an image forming apparatus, an image compressing method, and a recording medium.
2. Description of the Related Art
In the related art, high-compressed PDF is known as a technique of increasing a compression ratio of a PDF file and achieving more improvement in image quality. In the high-compressed PDF, a technique of dividing an image into a character area and a picture area and performing compression processes (MMR, JPEG, and the like) which are each suitable for one of the character area and the picture area, to realize high compression is known.
A technique of determining attributes of an original as a whole is generally referred to as an original type recognition technique. In creating a high-compressed PDF file, it is also known that an original type is determined using the original type recognition technique to switch processing (for example, a threshold value of a binarization process is switched or an appropriate compression method is selected) to be suitable for the original type.
In creating a high-compressed PDF file, there are following original types as original types which are expected to achieve improvement in image quality by switching processing to be suitable for the original type determined using the original type recognition technique.                Only-character original        Newspaper original        Thin original        
Particularly, with a recent increase in environmental consciousness, the number of cases in which an original is copied or printed in a toner save mode in reproducing an image using a copier increases. When a printed image in the toner save mode is scanned as an original and a high-compressed PDF file is created in this way, the original becomes a “thin original.”
However, according to the original type recognition technique according to the related art, there is a problem in that a determination circuit is necessary for each original type and processing costs increase. There is also a problem in that the original type recognition technique and the compression technique according to the related art cope with an “only-character original” and a “newspaper original,” but do not cope with the other original types (for example, a “thin original”).